In a double study, you are enrolled in at least two degree programs at a university at the same time.
This is the case, for example, with provisional enrollment in a Master degree program when transitioning from a Bachelor to a Master program within the same university. Until the end of the semester in which you were provisionally enrolled in the Master degree program, you are enroled in two degree programs simultaneously.
Until the end of the semester of provisional enrolment in the Master degree program, you will be studying twice in two degree programs.